Method of generating steam from waste heat of slag.



RALPH BAGGALEY, OF PITTSBURG, PENNSYLVANIA.

METHOD OF GENERATING STEAM FROM WASTE HEAT OF SLAG- Specification ofLetters Patent.

Eatented March 12, 1907.

Application filed October 14, 1904. Serial No. 228,486.

, Pittsburg, in the county of Allegheny and State of Pennsylvania, haveinvented a new and useful Method of Generating Steam from the Waste Heatof Slag, of which the following is a full, clear, and exact description.

The object of my invention is to utilize successfully the waste heat ofslag for the generation of steam, and particularly slag that resultsfrom the smelting of copper ores in a blast-furnace.

Molten slag is corrosive and injurious to all metals when it comes intocontact with water-j acketed surfaces or with heavy metal walls or withWalls of some refractory material, and it instantly forms skulls whichconstitute partitions between the body of molten material and the walls.Such slag skulls are non-conductors of heat, and it is most difficult totransmit heat through them from a body of molten slag to the watercontained in the boiler, so as to produce effective steampressure. Thesefacts make it diflicult to utilize by one operation more than a smallperclentage of the contained units of heat in the s ag.

Notwithstanding the formation of heatnon-conducting skulls on the wallsof a boiler and around water-tubes, I have discovered that if thefeed-water be preheated suflicient heat will be transferred from theslag through the skulls to the preheated feed-water in the water tubesto generate steam, wherefore the preheating of the feed-water is animportant feature of the present invention.

There is a great differencesay 50 Fahrenheit-in the temperature of waterthat may be used for the generation of steam such, for instance, as thetemperature in winter and in summer. An apparatus that may Worksuccessfully in the summer-time may fail in the winter-time, owing tothe great difference in the temperatures at which the feedwater might befed into the boiler. The problem will be greatly simplified if the feedwater can be delivered into the boiler at uniform temperatures in Winterand in summer, and if the feed-water is delivered into the boiler at auniform temperature of, say, 212 the mere addition of 40 or 50 of heatafter it has been delivered into the boiler will sufiice to produceefl'ective steam-pressure for actual work. In contradistinction to thissuppose water during the severe winter is delivered into the boiler at,say, 32 Fahrenheit, the amount of heat that must be transmitted from theslag to such cold water after it is in the boiler will be so great as torender the process impracticable. I have discovered these difficultiesin a long series of investigations, and the prevention of thesedifliculties constitutes the essence of my present invention. Toaccomplish this result, I utilize varying proportions of the waste heatproduced by the slag to bring the temperature of the feed-water up toapproximately 212 Fahrenheit in any convenient vessel or apparatussuitable for the purpose and thereafter I deliver such preheatedfeed-water into a suitable slag-boiler or slag steam-generator suitablefor the purpose, so as to further augment the temperature under pressureand in a confined vessel and to make such pressure available for use inlieu of steam-pressure produced through the combustion ofcarbonaceousfuel.

It will of course be understood that the slag which is fed to the boileror steam-generator is maintained out of contact with the water either bybeing directed around the ex-' terior of the boiler-shell or passedthrough tubes in the boiler in the manner of an ordinary fire-tubeboiler.

Feed-water as drawn from nature may be at a minimum temperature of 32Fahrenheit, or freezing. Its temperature may be raised in an open vesselat sea-level to approximately 212 Fahrenheit. In other words, about 180may thus be added toits temperature, or if the total temperature be 1raised under pressure to 344 Fahrenheit an effective workingsteam-pressure of one hundred and twenty-five pounds per square inch maybe produced. One hundred and eighty degrees of temperature may thus besupplied to feed-water in an open vessel and 120 may thereafter be addedto it under pressure in producing one hundred and twenty-five pounds ofeffective steam-pressure. The delivery of these heat units in an openvessel is comparatively easy to accomplish, while the delivery of theremaining 120 under pressure I have found from my experiments isdifficult.

It is of great importance that the waste heat units derivable fromblast-furnace slag should be utilized to the utmost extent, as

this steam-power is desirable for many pur poses. It isthereforeimportant that in conducting this method of generatingsteampressure all available heat units be utilized. After the congealedslag has been discharged from the steam-generator it will necessarilystill contain available heat units to an important extent. Thetemperature of this discharged congealed slag will rarely fall below 400Fahrenheit at the instant of its discharge, and it may easily exceed 900Fahrenheit, according to the rapidity with which it is discharged fromthe molds or receptacles of the steam-generator. Inasmuch as water at344 will produce approximately one hundred and twenty-five poundssteam-pressure, the spent slag after it is discharged from the steamgenerator may be advantageously utilized in heating the feed-water in anopen vessel. My preferred practice would be to utilize such spent slagto the utmost in heat ing the feed-water and thereafter using so much ofthe molten slag as might be found necessary in raising the temperatureof the feed-water in the open vessel to approximately 212. Thereafter Iutilize as much more of the molten slag as might be found necessary toraise the temperature while the feed-water was contained in a closedvessel under pressure (about say one hundred and twenty-five poundspressure or 344 Fahrenheit) or to any other pressure either more or lessthat might be found convenient for use in the particular service towhich my present invention is adapted.

The importance of the method herein described will be apparent when itis considered that if approximately thirty-four per cent. of the heat ofslag resulting from the operation of any copper plant is successfullyutilized it will furnish all the power required to operate such plant.In so far as I am aware no successful attempt has heretofore been madeto utilize the slag resulting from the smelting of copper ores. Theproblem of utilizing this slag is quite different from that of utilizingthe slag from iron blast-furnaces. In. the first place, with aniron-smelting furnace the slag is drawn off periodicallyi. (2., once inevery six or eight hoursand therefore its continuous utilization in thegene ation of steam is extremely difli cult. In the operation ofcopper-smelting, however, the slag flows in a practically continuous anduninterrupted stream from the forehearth. I am able, therefore, toutilize portions of this slag successively and continuously in themanner described. Furthermore, the slag from an iron-furnace is largelya silicate of lime, alumina, &c., practically devoid of iron. On theother hand, copper blast-furnace slae's may and do contain from twentyper cent. to fifty-five per cent. of iron. F or this reason they aremuch more efficient in supplying I however, prior attempts to utilizethese 'slags l have not been successful, owing in part to the l enormousshrinkage of these slags in cooling, amounting to approximatelyone-quarter inch per foot, to the corrosive nature of the slag whichcontains elements capable of dissolving almost any of the refractoriesfound in nature, and to the rapid forn'iati on of nonconducting skulls.It has therefore been impossible to maintain the slag in any oneoperation in such condition and relation to the water as to bring thelatter to the proper steam generating temperature, especially withinboilers, These difliculties I avoid in large measure by bringing thefeed-water to a high temperature in an open vessel, using for thispurpose the spent slag which has been passed rapidly through thegenerator, together with as much fresh slag as may be necessary.

1. The herein-described method. of utilizing slag from copper-smeltingfurnaces for the generation of steam, \vhicl'i consists in utilizing aportion of the slag to preheat feedwater to a relatively high tempoature before it enters the generator, and completing the heating withinthe gei'ierator by the further use of slag out of direct contact withthe water; substantially as described.

2. The metl'iod herein described which consists in taking a portion ofthe molten slag from a furnace, heating therewith water not underpressure, and taking the remainder of the slag and heating said waterunder pres sure and out of direct contact therewith for the generationof steam; substantially as do scribed.

3. The method herein described which eonsists in taking a portion of themolten slag from a furnace, heating therewith water not under pressure,and taking a portion of the remainder of the slag and heating said waterunder pressure and out of direct contort therewith for the generation ofst am; substantially as described.

4-. The method of utilizing slag from copper-smelting furnaces for thegeneration of steam, which consists in preheating feed-water in an openvessel to a relatively high temperature by the use of spent slag from asluggcnerator and also by molten slag from the furnace, and completingthe heating under pressure in a slag-generator wherein the slag and.water are maintained out of mutual contact; substantially as described.

5. The herein-described method of generating steam which consists inprelueating feed-water by means of hot slag, feeding the preheatedfeed-water to a stcam-generater. and passing hot slag through thegenerator out of contact with the water.

6. The herein-deseribed. method of generating steam which consists inintroducing heat. Notwithstanding these advantages, 1 preheatedfowl-water? into a sternn-generat u,

and passing hot slag through the generator izing the spent slag from thegenerator to out of contact with the water to generate preheatfeed-water. I: steam by radiation from the slag to the water. Intestimony whereof I have hereunto set 7. The herein-described method ofgenermy hand. 5 ating steam which consists in passing hot I RALPHBAGGALEY.

slag through a steam-generator out of oonitnesses: tact with the Waterto generate steam by ra- JOHN MILLER,

diation from the slag to the water, and util- H IVLCORWIN.

